So You Think You Know CSI

by Napoleon C. Reyes

The popularity of the television series CSI has raised public awareness of the different forensic techniques used in investigating crimes. The series regularly features police crime scene analysts cracking criminal cases through the use of various forensic techniques, such as DNA testing, fingerprint analysis, and firearms and bullets identification. Unfortunately, CSI has also misled viewers into thinking that all forensic techniques that they see on the show are real science and that forensic evidence are infallible. Nothing could be further from the truth.

An independent committee formed by the U.S. National Academy of Sciences to identify issues pertaining to forensic science has found that many forensic techniques currently used in investigating crimes have never been exposed to stringent scientific scrutiny. In a document released in August 2009, entitled Strengthening Forensic Science in the United States: A Path Forward, the committee declares that with the exception of nuclear DNA analysis, “no forensic method has been rigorously shown to have the capacity to consistently, and with a high degree of certainty, demonstrate a connection between evidence and a specific individual or source” (Committee on Identifying the Needs of the Forensic Sciences Community [henceforth, Committee], 2009, p. 7). It states that the interpretation of forensic evidence “is not always based on scientific studies to determine its validity” (p. 8) and that some non-DNA forensic tests “do not meet the fundamental requirements of science, in terms of reproducibility, validity, and falsifiability” (p. 43).

For example, the traditional method of fingerprint analysis for assessing individualization (i.e. the conclusion that a fingerprint comes from a single unambiguous source) was found to be based largely on human interpretation and is, therefore, highly subjective. Conclusions may differ from examiner to examiner. In fact, even experienced examiners have been shown to disagree with their own conclusions when the fingerprint examination is presented in a different context some time later (Dror & Charlton, 2006). Despite this, fingerprint examiners regularly testify in absolute terms, claiming that matched fingerprints can only come from one and only one person. The committee points out that:

Given the general lack of validity testing for fingerprinting; the relative dearth of difficulty proficiency test; the lack of a statistically valid model of

fingerprinting; and the lack of validated standards for declaring a match, such claims of absolute, certain confidence in identification are unjustified (Committee, 2009, p. 142).

According to the committee, no peer reviewed scientific studies have ever been done to prove the basic assumption that every person’s fingerprint is unique.

Other forensic techniques that were found to be questionable were bite-mark analysis, firearms and bullets identification, microscopic hair analysis, and burn pattern analysis.

Experience has shown that the misuse of forensic evidence could lead to tragic ending. In 2004, Cameron Willingham was executed in Texas after being found guilty of the arson-murder of his three young children. The primary evidence that led to his conviction was the fire investigator’s conclusion that the burn patterns found on the crime scene were telltale signs of arson. This conclusion has since been shown to be flawed.

In the same year, the FBI arrested Brandon Mayfield in Oregon in connection with the March 11, 2004 bombing in Madrid, Spain. The bombing killed nearly 200 people. Fingerprint examiners matched Mayfield’s known fingerprint to the partial latent fingerprint obtained from the crime scene and concluded that he was involved in the bombing. The problem was Mayfield had never been to Spain. Spanish authorities subsequently determined that the partial print belonged to another person. Mayfield sued the U.S. government and the latter settled for $2 million.

It is not yet clear how the committee’s findings will affect the criminal justice system. For years, police, prosecutors, judges, and lawyers have relied on forensic techniques under the assumption that they are real science and that forensic evidence are infallible. Now that we know that this is not true, steps must be undertaken to correct this assumption and prevent other miscarriage of justice. Additional research must also be done to put the science into forensic science.

References

Committee on Identifying the Needs of the Forensice Sciences Community. (2009).

Strengthening Forensic Science in the United States: A Path Forward. Retrieved from

https://www.ncjrs.gov/pdffiles1/nij/grants/228091.pdf

Dror, I.E., & Charlton, D. (2006). Why experts make errors. Journal of Forensic

Identification, 56(4), 600-616.

PBS. (2012). The Real CSI. Frontline. Retrieved

from http://www.pbs.org/wgbh/pages/frontline/real-csi/